Conventional thermoplastic polyolefin (“TPO”) based roofing membranes can be made up of three layers. As shown in FIG. 1, a typical TPO based roofing membrane 100 can have an upper layer 110 that is generally a TPO sheet, sometimes referred to as a “cap layer”, which can be formulated with ultraviolet absorbers and stabilizers, thermal stabilizers, pigments, fire retardants and the like. Typically, the upper layer 110 can be formulated to provide for long term stability in an outdoor environment. The bottom layer 130 of a TPO roofing membrane can also be a TPO sheet, sometimes referred to as a “core layer”, and generally can contain fewer or lower concentrations of stabilizers.
The central layer 120 of a TPO roofing membrane can typically be a fabric scrim that acts as a reinforcement to improve the physical performance of the roofing membrane 100. The fabric scrim 120 can contribute significantly to the tensile strength of the roofing membrane 100 and provide for dimensional stability. Typically, the fabric reinforcement can be a polyester based scrim. Glass based scrims can also be used where additional weight or improved dimensional stability may be required.
The three layers can be laminated together at elevated temperatures such that the upper layer 110 and bottom layer 130 can be joined or fused together through the interstices of the scrim of the middle layer 120.
Roofing membranes can provide more benefits than just protection from the weather. In addition to aesthetic aspects of residential roofing material design, both residential and commercial roofing can now provide advantages to the energy usage of buildings and homes. By providing roofing membranes with higher reflectance, it can be possible to lower the heat gain experienced by a building. Such reflective systems are referred to as “cool roofs” and provide for lowered cooling demand for building interiors.
TPO roofing membranes are mostly used on low slope roofs that can have pitches of less than approximately two inches vertical rise over an approximately twelve inch horizontal distance. One advantage of TPO membranes compared to traditional asphaltic systems can be their high total solar reflectance (“TSR”), which can be achieved through various means including the incorporation of titanium dioxide.
The TSR can indicate how much of the sun's ultraviolet, visible and infrared energy (i.e., solar flux) is reflected. TSR can be defined as the fraction of solar flux reflected by a surface expressed as a percent or within the range of 0.00 and 1.00. Measurement can be done using the methods described by the American Society for Testing and Materials (“ASTM”) Standard E903, ASTM C1549 or ASTM E1918. ASTM E903 measures TSR over the wavelength range 250 nm to 2500 nm using integrating spheres. By using a commercial portable solar reflectometer that can be calibrated using specimens of known TSR, ASTM C1549 can determine TSR from measurements at four wavelengths in the solar spectrum: 380 nm, 500 nm, 650 nm and 1220 nm. ASTM C1549 shows the comparison results between the C1549 and E903 methods. The solar reflectance results at air mass 1.5 measured per ASTM C1549 are generally 1.9% greater than those obtained with SSTM E903. ASTM discontinued E903 in August 2005 in accordance with section 10.5.3.1 of the Regulations Governing ASTM Technical Committees, which requires that standards shall be updated by the end of the 8th year since the last approval date. ASTM E1918 covers the TSR measurement for various horizontal and low sloped surfaces and materials in the field, using a pyranometer. This test method can be used when the sun angle to the normal from a surface is less than 45 degrees. For commercially available white or very light color TPO membrane, TSR is typically 0.70 or higher.
Roofs that can be seen from the ground and roofs that are overlooked by taller buildings are generally unattractive when white and highly reflective. Therefore, manufacturers have begun to use color pigments for those TPO roofing membranes that will be viewed, or that are required to have aesthetic value. However, such colored membranes have significantly degraded TSR values, compared to white, depending on the darkness of the pigment used.
Some TPO roofing membranes have a “cool color” pigment technology that reflects more infrared radiation than would be expected for a given color. However, these roofing membranes provide only a marginal improvement over standard colored TPO roofing membranes.
The cap layer, or upper layer, of a roofing membrane represents a very significant portion of the cost of a roofing membrane. Further, in hot climates, the solar reflectance of colored TPO membranes can affect the heat gain experienced by a commercial or residential building. Also, the long term weathering performance and color fastness of the cap layer of colored TPO roofing membranes are critical for long term waterproofing and for aesthetic appearance.
Throughout the figures, the same reference numerals and characters, unless otherwise stated, are used to denote like features, elements, components or portions of the illustrated embodiments. Moreover, while the subject invention will now be described in detail with reference to the figures, it is done so in connection with the illustrative embodiments. It is intended that changes and modifications can be made to the described embodiments without departing from the true scope and spirit of the subject disclosure.